Yep, although that wasn't really the point of my excercise. :-) I'd write that one a little differently:

my %xlat = (
    F => '|',
    S => '^',
    T => '&',
    R => '~'
    E => '\\',
);

while( m/ \G .*? \\([FSTRE])\\ /gsx ){
    substr $_, pos() - 3, 3, $xlat{ $1 };
}
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Update: same change as in parent node update applies.